This invention relates generally to a coaxial dielectric resonator of the TEM mode for VHF and/or UHF band, and more particularly to such resonators which are small in size, providing high Q.
Recently, intensive research for miniaturizing filters and resonators used in VHF and/or UHF band and raising efficiency thereof has been carried on. For this purpose, it is earnestly expected to realize a small resonator having high Q (low loss).
As a small resonator for VHF and/or UHF band, there is known a quarter wavelength coaxial dielectric resonator. This conventional resonator comprises coaxially arranged cylindrical outer and inner conductors and having a dielectric filled in the space between the outer and inner conductors. One end of the outer and inner conductors is shorted together by a shorting conductor, and at other end of the inner conductor, an electrode for adjusting the resonance frequency of the resonator is mounted. The dielectric with outer, inner and shorting conductors is inserted into a case and convered by a lid on which an adjustable screw is mounted for adjusting resonance frequency with the electrode.
The above-mentioned conventional resonator has been shortened in length as expressed by 1/.sqroot..epsilon.r, wherein .epsilon.r is the specific inductive capacity of the dielectric used. The resonance frequency of the resonator is adjusted by varying a gap distance between the electrode and the screw which constitute a capacitor.
However, in the resonator, the screw is mounted at outside of the lid so that the loss of space is unavoidable when the resonator is assembled in an apparatus. Furthermore, the resonance frequency is made variable by varying the gap distance because of the screw touching other parts of the apparatus.
In addition, when a filter is assembled by the use of the resonator, especially when stepped impedance type is used, unnecessary resonance is apt to occur because of unsufficient ground of the resonator.